1. Field of the Invention
The present invention relates generally to a warning system for use in automotive vehicles More particularly, the present inventions relates to a brake master cylinder assembly having a warning signal system for producing a signal in response to excessive brake pedal travel.
2. Description of the Related Art
In typical automotive braking systems, a brake pedal is connected to a hydraulic master cylinder through a connecting linkage. When the vehicle operator depresses the brake pedal, an actuator rod contacts a piston disposed within the master cylinder. The piston forces hydraulic brake fluid contained in the braking system under pressure. The pressure is transmitted through a rigid tubing and flexible lines to each wheel of the vehicle to effect braking at each wheel.
In recent years, most vehicles have utilized a dual master cylinder having two cylinder reservoirs contained within a brake master cylinder assembly Each of the cylinders operates independently through separate brake lines, one actuating the front brakes and the other actuating the rear brakes. Also, it is known to utilize one cylinder to actuate the right front, left rear brakes while the second cylinder operates the left front, right rear brakes. These independent braking operations function as a safety feature in that should one system fail, the other system operates to effect the braking of the vehicle. If there is a failure in one of these systems, possibly due to a leak in one of the hydraulic pressure lines, the brake pedal will be depressed beyond a predetermined distance. The increased pedal travel required to compensate for the loss of the failed portion of the brake system may give warning that a partial brake failure has occurred in that the operator of the vehicle may notice a different "feel" to the brake pedal. However, this feel by the vehicle operator is an unreliable indication of brake failure, since increased pedal travel may be due to variables other than a failure in the hydraulic system of one of the brake systems.
For example, increased pedal travel may be due to a condition known as brake fade. Brake fade may occur when the brakes become overheated during multiple, extensive applications of the brakes such as during panic stops from freeway speeds in heavy traffic or braking down a long hill while pulling a trailer. When the brakes become overheated, the brake linings become compressible, or "spongy", and lose their ability to effect stopping of the wheel. The vehicle operator must push continuously harder on the brake pedal to compensate for the compressibility of the linings, thus forcing the piston in the master cylinder beyond its predetermined travel limit. In the absence of a warning device indicating to the vehicle operator that the brake system integrity has been breached, the driver relies solely upon the "feel" of the brakes to determine a possible problem.
One known method for warning the vehicle operator of a failure of one of the brake systems due to a leakage of the hydraulic fluid in one of the lines is by the use of a pressure differential valve. The valve generates a warning signal, received by the vehicle operator, whenever one of the brake systems has a pressure drop. However, the pressure differential valve only acts in response to a pressure drop and not to brake fade.
Other fluid pressure responsive devices have been proposed for generating a signal in response to pressure changes within a housing. For example, U.S. Pat. No. 3,611,220 discloses a fluid pressure responsive device having two magnets with like poles facing each other. A first magnet is mounted with a piston to be movable toward the second magnet in response to fluid pressure, causing the second magnet to repel and, consequently, exciting a magnetic responsive monitor. The system utilizes two magnets and relies upon the repulsion of the magnets to effect a warning. The system may not be suitable for use in the confines of a master cylinder assembly. Also, the presence of two magnets may interfere with the operation of the master cylinder, resulting in failure of the brake system. The '220 system responds to pressure changes on opposite sides of a filter and does not teach or suggest the use of such system in a brake master cylinder assembly.
U.S. Pat. No. 3,564,175 discloses a magnetic pressure responsive switch for use with a filtering mechanism, the switch having a magnetic piston movable towards a partition in a housing in response to a predetermined pressure differential between two passages. An electrical switch is mounted on the opposite side of the partition and is actuated by the magnetic piston as a pressure differential draws the piston towards the partition. The '175 patent fails to teach or suggest the use of such system in a brake master cylinder assembly and such a system would give no indication of excessive brake pedal travel due to brake fade since the '175 system requires a pressure differential to move the piston.
The present system provides a means of warning a vehicle operator of excessive brake pedal travel due to brake system failure, brake fade or hydraulic brakeline failure by providing a master cylinder assembly having a magnetic member disposed on a piston within the master cylinder chamber. The magnetic member actuates a magnetic responsive switch as the piston moves beyond a predetermined distance within the master cylinder.
It is a feature of the present invention to provide a master cylinder assembly which warns the vehicle driver of either a low brake fluid level or excessive brake pedal travel by an inexpensive and reliable system utilizing a magnetic responsive switch, a piston having a magnetic member within the housing of the master cylinder and a float assembly in the master cylinder reservoir.
It is an object of the present invention to provide a brake pedal travel warning system which generates a warning signal to the vehicle operator without relying on unreliable "feel" of the brake pedal by the operator.
It is an advantage of the present invention to provide a brake pedal travel warning system which is economical to produce and reliable in service with a minimum of moving components.